The present invention relates to a method for traffic control in a communication system transferring traffic units, the method comprising the steps of maintaining a continuously changing quantity for the traffic units, the value of the quantity at any one time determining whether an individual traffic unit can be accepted to be forwarded; changing, at accepted traffic units, the value of said quantity so that a traffic density lower than a specific predetermined value changes the value of the quantity in a first direction but no more than up to a predetermined first limit, and a traffic density higher than said predetermined value changes the value in a second direction; and beginning rejection of traffic units as the value of the quantity in said second direction reaches a specific predetermined second limit. The invention further relates to traffic filters for limiting traffic in a communication system forwarding traffic units, such as cells.
The solution according to the invention may be utilized for example in measuring cell traffic in an ATM network, but it is applicable in connection with other kind of traffic as well, for example in call transfer, as will be disclosed below. Due to the many operational environments, the cells, packets, calls etc entities transferred in the system will below be referred to with a general term xe2x80x9ctraffic unitxe2x80x9d.
Usually, at the connection establishment or at the connection set-up phase, the parameters to be complied are agreed upon. Typical connection parameters include traffic maximum rate and average rate. From the point of view of the network, it is not certain that the parameters agreed upon would automatically be complied on each connection. A reason for this is that it is difficult for a user to know accurately the nature of the traffic in advance. E.g., the average bit rate of a compressed video signal may be very difficult to determine in advance. The subscriber equipment may also be faulty or the users may, quite on purpose, to underestimate their bandwidth requirements to keep the costs lower. Due to e.g. the above reasons, it must be ensured at the network-subscriber interface that the traffic sources stay within the limits agreed upon at the connection set-up phase.
Various kinds of mechanisms have been developed for traffic source policing, most of which police the average and maximum rates of the traffic source and the duration of active periods. One of such mechanisms is a so-called xe2x80x9cleaky bucketxe2x80x9d principle. The principle of leaky bucket is disclosed e.g. in the reference Raif O. Onvural: Asynchronous Transfer Mode Networks, Performance Issues, Arctech House Inc., 1994 (ISBN 0-89006-662-0), Chapter 4.5.1. The leaky bucket principle is used e.g. by the GCRA algorithm (Generic Cell Rate Algorithm) of an ATM (Asynchronous Transfer Mode) network UPC (Usage Parameter Control) function, the GCRA being used to police that cell traffic is in accordance with the traffic agreement of the connection in question.
The aforementioned prior art mechanisms are not, however, the best possible e.g. in such applications in which a specific (smaller) information unit, such as a cell, is critical from the point of view of correctly receiving a larger information unit. In such a case, losing a smaller information unit e.g. an AAL (=ATM Adaptation Layer) frame might lead to having to retransmit a larger amount of information. To take an example, if the data stream has been divided into xe2x80x9csegmentsxe2x80x9d that are compressed and encrypted so that each encrypted data unit is hundreds of cells long, the loss of one or more cells may lead to the receiver being incapable of reconstructing the data unit, and all the cells of the unit in question have to be retransmitted.
Utilizing prior art policing mechanisms in connection with embodiments of the type described above results in wasting the network resources. This is because the known mechanisms limit traffic so that the accepted traffic is always in accordance with the traffic agreement (i.e. only traffic units violating the traffic agreement are rejected), whereby rejecting a specific portion easily results in that also previously accepted traffic units have to be retransmitted.
It is an object of the present invention to provide, in as simple as possible a manner, an improvement on the drawback set forth in the above. This object is achieved by the method according to the invention, which is characterized in that the value of the quantity is also changed at rejected traffic units in said second direction, but no more than up to a specific predetermined third limit, and that when the value of the quantity is between the second and the third limit, it must again alter in said first direction up to at least said second limit before traffic units are accepted. The second embodiment of the invention relates to a method for traffic control in a communication system forwarding traffic units, the method comprising the steps of calculating a Theoretical Arrival Time (TAT) for the next traffic unit to arrive, whereby the actual arrival time of the incoming traffic unit determines whether an individual traffic unit can be forwarded; changing, by means of accepted traffic units, the theoretical arrival time so that a traffic density lower than a specific predetermined value changes the theoretical arrival time less than a traffic density higher than said predetermined value; and rejecting a traffic unit arriving before the TAT to the extent of a specific predetermined instant of time (TAT-L). This invention is characterized in that also rejected traffic units are utilized in changing the theoretical arrival time, but no more than up to a specific predetermined limit (time+H).
The invention also relates to a filter for limiting traffic in a communication system forwarding traffic units, such as cells, the filter comprising means for maintaining the continuously changing quantity whose value at any one time determines whether an individual traffic unit can be accepted to be forwarded; means for changing the value of said quantity at accepted traffic units so that a traffic density lower than a specific predetermined value changes the value of the quantity in a first direction but no more than up to a predetermined first limit, and a traffic density higher than said predetermined value changes the value in a second direction; and means for rejecting traffic units as the value of the quantity reaches and exceeds in said second direction a specific predetermined second limit. The invention is characterized in that it further comprises means for changing the value of the quantity at rejected traffic units in said second direction but no more than up to a specific predetermined third limit.
The invention further relates to a filter for limiting traffic in a communication system forwarding traffic units, such as cells, the filter comprising calculating means for calculating the theoretical arrival time for the next traffic unit to arrive; comparing means for comparing the actual arrival time of the arriving traffic unit to the calculated theoretical arrival time and the time dependent thereupon; and decision-making means responsive to the comparing means for determining whether an individual traffic unit can be accepted to be forwarded. The invention is characterized in that the calculating means are adapted to change the theoretical arrival time also at rejected traffic units but no more than up to a specific predetermined limit.
The idea of the invention is to modify the prior art policing mechanisms into low-pass direction so that they are able to filter all traffic from a traffic source not complying with the parameters agreed.
The solution according to the invention provides, in a simple manner, a policing mechanism by means of which it is possible to save network bandwidth in connection with the types of traffic sources described above.